The present invention relates to a method of and an apparatus for punching a substrate and, more particularly, to a punching method and a punching apparatus for forming through holes in a ceramic green sheet which is used as a material of, for example, laminated substrate.
In, for example, U.S. Pat. No. 4,209,129, for punching out through holes in a ceramic green sheet, the punching is effected by an upper die set which is driven vertically reciprocated through an eccentric mechanism which converts a rotational motion of a motor into a vertical linear motion.
Recently there has been a great demand for a punching method and apparatus which permits an easier, quicker and more flexible change and setting of working conditions such as the positions of the top and lower stroke ends of the upper die, as well as the stroke length of the upper die, in order to meet a wide variety of through hole patterns and types of the die.
Additionally, it is to be pointed out that the through holes, after the punching, tend to be clogged with chips due to stickiness of the green sheet material. In case of a laminated substrate, the product must be rejected as being unacceptable even when one of the through holes is clogged. In order to avoid this problem, it is necessary to take an additional post-machining step to remove any clogging of the through holes. This post-machining, however, is quite troublesome and difficult to conduct because the through holes in the laminated ceramic substrate are extremely fine and the green sheet is deformable and flexible. Additionally, the post-machining undesirably degrades the dimensional precision such as the pitch of the through holes.
Accordingly, an object of the invention is to provide a punching method and apparatus for forming through holes in a workpiece which is mainly a ceramic green sheet, at a high efficiency and without suffering from clogging of the through holes with chips.
To this end, according to the invention, not only the positioning of the workpiece but also the driving of the upper die set are conducted by servomotors. The speed and timing of operation of the servomotors are controlled in accordance with a prestored program in a microcomputer, so as to attain a high speed and efficiency of operation. Additionally, a hole clearing operation is conducted immediately after the punching so that the chip remaining in the punched through hole, if any, is forced out therefrom by the same punch.
According to one feature of the invention, X-Y tables are disposed under a die, and the green sheet on a support member secured to an X-table, is movable between an upper die set and a lower die set of the die.
According to another feature of the invention, the upper die set forms the through holes in the green sheet by the punch in its downward stroke and then, before or after the upper die set reaches an end of its lower stroke, the microcomputer issues commands to instantaneously stop and reverse the servomotor to raise the upper die set.
Accordingly to still another feature of the invention, after the edge of the punch comes out of the green sheet during an upward stroke thereof, the indexing operation of the X-Y tables is started before or after the upper die set reaches an end of the upper stroke.
According to a further feature of the invention, after the edge of the punch projects out the green sheet during an upward stroke thereof, the downward and upward strokes of the upper die set are conducted again as required without conducting the indexing operation of the X-Y tables before or after the upper die set reaches the end of the upper stroke, so that the same through hole is punched two or more times by these punches.